Biological Reduction of Structural Iron in Sodium‐Nontronite

Abstract To test the possibility that the structural Fe 3+ in clay minerals can be biologically reduced, nontronite was mixed with sucrose and an aqueous extract from a Chinese paddy soil and incubated for 14 d at room temperature. Reflectance spectra, x‐ray diffraction patterns and Fe 2+ /Fe 3+ ratios were determined for the nontronite in the mixture and for the nontronite in its nonreduced and chemically reduced states. It was found that the results for the nontronite in the mixture resembled those for the chemically reduced nontronite but differed markedly from those for the nonreduced nontronite. Therefore, it was concluded that microorganisms from the soil extract were able to reduce the structural Fe 3+ in nontronite.